What is the Sun? The Sun is a star, a massive celestial body that converts matter into energy. It is the largest object in the solar system and is at its center; the gravitational field it exerts pulls the Earth, and all other planets and objects in the solar system, causing them to orbit it. The Sun produces energy by fusing hydrogen atoms in its core, producing helium. This continuous nuclear reaction emits tremendous amounts of energy, which is released as solar radiation. This radiation reaches the Earth and provides most of the energy needed to sustain life. Can you tell me more about suns from other solar systems?
Sure thing!
The nearest star system to us is Alpha Centauri: A star system which consists of 3 stars. These stars are Rigil Kentaurus, Toliman, and Proxima Centauri. Of these stars, Proxima Centauri is significantly closer to our Solar system than the others.
Another notable star is Polaris (a.k.a. the North Star), which is the brightest star in the Ursa Minor constellation. This star has the property that it is extremely close to being in line to the Earth's rotational axis. Thus, in the northern hemisphere, it is a star that has historically been used by sailors to navigate at night. Additionally, when you look up at the night sky for a long enough period of time, other stars will appear to rotate around it.

In general, when it comes to stars, most are classified according to a Morgan-Keenan spectral class: a classification system which measures stars based on their heat as well as their luminosity. In this system, our Sun has a spectral type of G2V which means that it has class G2 (a temprature of )and magnitude V. Here, the letter G means that the star has a temperature between 5,200 Kelvin(K) and 6,000K. The number (between 0-9) following the G further indicates a subsection of said range with 0 being the hottest and 9 being the coolest. (Thus, each subsection is divided evenly into 10 parts.) The two following the G in this case further indicates that the Sun's temperature sits between 5,760K and 5,840K (Indeed, the surface temperature of our sun is 5,778K.)
The letter(s) after the number indicate the luminosity. In this case, the V indicates that the Sun is part of the main sequence of dwarf stars.

I hope these responses were helpful.
Suns from other solar systems are much like our own Sun, though they come in a wide variety of sizes, ages, compositions, and temperatures. The stars in other solar systems form in much the same way as our own: gravity pulls together clouds of gas and dust until they collapse under their own weight, and the resulting heat and pressure in the core cause nuclear fusion reactions to take place. These reactions provide the energy that powers the star, and the type of star formed depends on its mass and composition. Some stars are much larger than our Sun, while some are much smaller. Additionally, stars can be much hotter or cooler than our Sun, depending on their age and composition.